Fig. 1 _a_, Basal membrane, with the cementing apparatus, of
_Coronula balænaris_; a small portion of the parietal
membrane, _p p p_, which coats the folded shelly walls, is
left adherent to the basal membrane.
_b_, the circumferential slip (shaded more darkly than the
rest to catch the eye), separating the basal from the
parietal membrane.
_c′ c′_, slips of basal membrane, formed at each period of
growth, and overlapping each other.
_s s s s s s_, the six sutures in the walls, separating the
six compartments, of which--
A is the basal margin of the rostrum,
C C that of the lateral compartments,
D D that of the carino-lateral compartments, and
E that of the carina.
_r_, _r_, rays or spokes of membrane, prolonged from the
circumferential slip, and running under the trebly folded
wall of each compartment, but here cut off; a similar ray
should run under each line of suture (_s_). These rays, at
their extremities, expand transversely; and the shape and
length of the rays may be judged of from the basal outline
of the folded walls given in Pl. 16, fig. 5.
The two cement-ducts, proceeding from each cement-gland,
debouch opposite the middle folds of the lateral (C C)
and carino-lateral (D D) compartments. The layers of
cement have been removed. N.B. There is one considerable
error in this figure, the two main trunks, connecting
the cement-glands, and meeting at the centre, have been
represented as forming a straight line, but in fact they
form a very open angle, as is correctly shown in fig. 1 _c_.
1 _b_, Diagram, representing a vertical section through a
portion of the basal and parietal membranes, with the
thickness of the membrane enormously exaggerated.
_z z z_, layers of cement, which, if the section had been
made in the line of the cement-ducts, would have been seen
proceeding out of these ducts, as is represented at (_t_),
where the section is supposed to have taken the above
course.
_c′ c′_, the slips of basal membrane.
_b_, the circumferential slip; beneath this the coarsely
dotted layer represents the cement, lately excreted, and
before it has acquired its proper transparent structureless
character, elsewhere represented by fine dots.
_p_, membrane externally coating the walls of the shell.
_t_, cement-ducts opening beneath the basal membrane.
1 _c_, The central portion of fig. 1 _a_, considerably
magnified.
_c′ c′_, slips of the basal membrane; but the shell, when
these were formed, was so young that the walls had not
acquired their folded structure; in the centre the
prehensile antennæ of the pupa may be obscurely seen.
_f_, the main cement-trunk, connecting the cement-glands.
_h_, a cement-gland, from which two cement-ducts proceed.
_a a_, cement-ducts (cut off), leading to opposite the middle
fold of the carino-lateral compartment.
_b b_, cement-ducts (cut off), leading to opposite the middle
fold of the lateral compartment.
_a′ b′_, a pair of cement-ducts, with their orifices opening
on the under side of one of the slips of basal membrane
(_c′_), at a point which once was opposite the middle of
the carino-lateral and lateral compartments. The orifices
of the other ducts, towards the centre, may be seen forming
straight lines.
2, Cement-ducts and one cement-gland of _Chelonobia patula_,
represented without the basal membrane, to which they
adhere: _f_, _f_, main cement-trunk; _g_, enlarged portion;
_h_, gland; _a_, _b_, the two ducts proceeding from this
gland, and bifurcating several times before debouching
on the under side of the basal membrane. Several other
cement-ducts, proceeding from other glands, are represented
just as they appeared under the microscope.
3, Cement-ducts and glands of _Tubicinella trachealis_,
represented without the basal membrane to which they
adhered: (_f_) (_f_), main cement-trunk, connecting the
several glands; _h_, cement-gland; _a_, cement-duct, with a
singular loop (_a′_) having two projections or rudimentary
branches; _b_, spur or rudiment of a second cement-duct;
_c_, third cement-duct.
4 _a_, Chain of cement-glands of _Balanus tintinnabulum_,
_with all the ducts removed_, _excepting those proceeding
from the last formed gland_, which latter correspond in age
with the last-formed zone of the shelly basis; the whole of
the basis having been removed by acid.
_f_, main cement-trunk connecting the glands.
_gh_, last-formed cement-gland.
_k_, _t_, two cement-ducts, proceeding from a great common
duct; one of these bifurcates at (_t_), and one branch
joins at (_t′_) the corresponding branch from the
corresponding gland.
_i i i_, circumferential duct, into which the ducts _k_, _k_,
_t_, _t_, _t′_ all enter.
_i′ i′_, branches proceeding from the circumferential duct,
which branch and sub-branch till they form a sheet (_z z_)
of cement-tissue on the outside of the basis of the shell.
4 _b_, two cement-glands of _Bal. tintinnabulum_ (this figure,
to match with 4 _a_, ought to have stood upside down),
taken from near the centre of the basis, greatly enlarged;
(_f f_), main trunk; (_g_), enlarged portion of the trunk;
(_h_), gland; _k_, _t_, two cement-ducts proceeding from a
common point, one of them (_t_) bifurcates, and gives off
a rudimentary branch, _t′_; _m_, a spur, or rudimentary
duct. The gland, _h_, has been pushed on one side, it
ought to lie over the enlarged portion (_g_). There is a
considerable difference between these two glands and that
(_gh_) represented in fig. 4 _a_; the neck of the gland in
the latter being elongated into a great common duct, and
the spur or rudimentary duct (_m_) being absent.